The development of fuel cells is intensifying, since it is said that fuel cells are a power generation system having good energy utilization efficiency. Among fuel cells, polymer electrolyte fuel cells are especially drawing attention due to their high power density and ease of handling.
For a fuel cell, which generates power through an electrochemical reaction between hydrogen and oxygen, it is essential to establish hydrogen supply means. One method for doing this is to produce hydrogen by reforming a raw material for hydrogen production such as a hydrocarbon fuel. From the viewpoint that supply systems of hydrocarbon fuels are already socially established, this method is more advantageous than methods in which pure hydrogen is used.
Examples of hydrocarbon fuels include city gas, LPG, gasoline, kerosene, light oil and the like. Since liquid fuels such as LPG, gasoline, kerosene and light oil are easily handled, stored and transported, and are inexpensive, these fuels are gaining attention as fuels for fuel cells. In order to use these raw materials for hydrogen production in fuel cells, hydrogen must be produced from the hydrocarbon. For this purpose, a hydrogen production apparatus equipped with at least a reformer is used.
In a hydrogen production apparatus, for example, a hydrocarbon is reacted with water in a reformer to decompose into mainly carbon monoxide and hydrogen. Then, a large portion of the carbon monoxide is reacted with water in a shift reactor to convert into hydrogen and carbon dioxide. Finally, the small remaining amount of carbon monoxide is reacted with oxygen in a selective oxidation reactor to turn into carbon dioxide. Further, since sulfur may be a poisoning substance for reforming catalysts or the like, in many cases a desulfurizer is provided for removing the sulfur in the hydrocarbon fuel.
When stopping such a fuel cell system, for the purpose of protecting the catalyst present in the hydrogen production apparatus and the like, purging with an inert gas, typically nitrogen, has been carried out. However, space is required to store nitrogen, and it takes time and effort to supply and manage nitrogen.
In order to break through such a situation, Patent Document 1 discloses a fuel cell power generation system which utilizes regenerable oxygen removal means for removing oxygen contained in air. Patent Document 1 is directed to providing purge means of a fuel cell power generation system where the means can easily supply an inert gas to be used for the purging of a fuel cell system and the means needs no component replacement and the like and is good in maintenance aspect.
In the art of Patent Document 1, although an inert gas cylinder or the like is unnecessary, air is fed to a deoxydizing column (oxygen removing means) from an air supply blower to reduce the oxygen concentration, and the purging is carried out using this oxygen-reduced gas. That is, purging is still carried out, and the shutdown operation cannot be said to be simple. Further, operation of the air supply blower needs to be continued even after finishing power generation, and thus the energy used for this purpose is wasted.
Patent Document 2 discloses an art which enables suppressing oxidation degradation of the catalyst in a hydrogen production apparatus with no purge operation upon shutting down the hydrogen production apparatus or a fuel cell system provided with the hydrogen production apparatus.    Patent Document 1: Japanese Patent Laid-Open No. 2002-280038    Patent Document 2: Japanese Patent Laid-Open No. 2005-179081